The present invention relates to a method of compressing data and storing the same in a memory, and a disk storage system having a cache memory to which the method is applied.
In recent years, a disk storage system having at least one disk storage device is commonly provided with a cache memory. In particular, most of disk array systems which use plural disk drives to thereby impart redundancy and to thereby increase in performance and resistance to failure have capacities of a few hundred gigabytes. So, they have cache memories of a capacity of several gigabytes.
In the disk storage system, the difference between the time required to access a recording medium and the time required to access the cache memory is very large. Therefore, the effect of improving a response time due to introduction of the cache memory is noticeably exhibited in the disk storage system. With increase in the capacity of the cache memory, the hit rate of the cache memory is improved and the response time is improved. On the other hand, the provision of the disk storage system with a cache memory of large capacity greatly increases the overall cost of the disk storage system.
Meanwhile, data compression technique is known as means that effectively uses less storage regions. According to a reference, for example, "Document Data Compression Algorithm" by Tomohiko Uematsu, CQ publishing Co., Ltd., pp. 227-244, data can be compressed to a capacity less than half the original data on the whole although the capacity depends on a compression algorithm or data to be compressed.